Several methods are provided to solve performance deterioration caused by inter-cell interference in an environment where one network provider not several network providers controls several cells.
As methods for controlling inter-cell interference, there are provided a method for removing interference by using different frequency bands having no interference in neighboring cells and a method for reducing interference affected to a neighboring cell by reducing the power used in a cell, which affects high interference to the neighboring cell, through proper power control while using the same frequency band.
In this case, if one (or carrier) channel of inter-cell interference control through power control is only used, the optimized power control for inter-cell interference control is that the lowest power and the highest power are controlled without properly reducing or increasing the power. This power control may be referred to as power on/off control, and power on/off state of each access point may be defined as a pattern.
FIG. 1 is a diagram illustrating a shape of a pattern control for controlling inter-cell interference if two cells are provided.
Referring to FIG. 1, if two access points are provided, a total of three possible patterns may be provided. In other words, examples of the three possible patterns include a ‘pattern 1’ that uses two access points, a ‘pattern 2’ that uses the first access point only, and a ‘pattern 3’ that uses the second access point only.
In case of the pattern 1, since two access points are turned on at the same time, inter-cell interference occurs. On the other hand, in case of the pattern 2 or the pattern 3, since only one access point is turned off, interference in the other cells may have a channel status. However, a problem occurs in that the number of data to be simultaneously transmitted from the pattern 2 and the pattern 3 is reduced from two to one.
The related art is intended to reduce performance deterioration caused by inter-cell interference of each of a plurality of access points owned by one network provider. In this case, inter-cell interference is controlled through a method for turning on or off each access point every time slot, that is, a method for determining a pattern every time slot.
Hereinafter, a method for controlling inter-cell interference of each access point will briefly be described in accordance with a pattern method.
First of all, for convenience of description, terms will be defined as follows.
N: means a set or the number of access points or cells
S: means a set or the number of users
Sn: means a set or the number of users who receive a service from an access point n
P: means a set or the number of patterns
Np: means a set or the number of access points turned on in a pattern p
Ss(t): means an average transmission rate obtained by a user s to reach a time t
rs,p(t): means an instantaneous transmission rate owned by a user s at a time t in case of a pattern P
α: means a parameter that controls efficiency of network and equity between users
β: means a constant required for update of the average transmission rate
Scheduling Algorithm for User (User Equipment) within AP and Pattern Selection
1. AP measures an instantaneous transmission rate rs,p(t) of a user for each pattern at the time of every time slot. Also, the AP notifies (or transmits) a central node (CN) of the measured instantaneous transmission rate rs,p(t). In this case, it is general that the central node and the AP are connected with each other by the wire. However, the central node and the AP may be connected with each other by the wireless.
2. The central node determines an optimized pattern p* of patterns that mean a turn on or off state of each AP as below on the basis of an instantaneous transmission rate of a user every time, through the following Equation 1.
                              p          *                =                                            arg              ⁢                                                          ⁢              max                                      p              ∈              P                                ⁢                                    ∑                              n                ∈                                  N                  p                                                                                                  ⁢                                                  ⁢                          [                                                max                                      s                    ∈                                          S                      n                                                                      ⁢                                                                            r                                              s                        ,                        p                                                              ⁡                                          (                      t                      )                                                                                                  [                                                                        R                          s                                                ⁡                                                  (                                                      t                            -                            1                                                    )                                                                    ]                                        α                                                              ]                                                          [                  Equation          ⁢                                          ⁢          1                ]            
3. An access point nεNp* turned on at the pattern p*(t) defined by 2 as above determines a user (or user equipment), who will receive a service, through the following Equation 2.
                              s          n          *                =                                            arg              ⁢                                                          ⁢              max                                      s              ∈                              S                n                                              ⁢                                          ⁢                                                    r                                  s                  ,                  p                                            ⁡                              (                t                )                                                                    [                                                      R                    s                                    ⁡                                      (                                          t                      -                      1                                        )                                                  ]                            α                                                          [                  Equation          ⁢                                          ⁢          2                ]            
4. The average transmission rate R(t) is updated in accordance with the following Equation 3 on the basis of the result of 3.
                                          R            s                    ⁡                      (                          t              +              1                        )                          =                  {                                                                                                                                                                                              (                                                          1                              -                              β                                                        )                                                    ⁢                                                                                    R                              s                                                        ⁡                                                          (                              t                              )                                                                                                      +                                                  β                          ⁢                                                                                                          ⁢                                                      r                                                          s                              ⁡                                                              (                                t                                )                                                                                                                                                        ⁢                                                                                                                                                                                              if                        ⁢                                                                                                  ⁢                        s                                            =                                                                        s                          n                          *                                                ⁡                                                  (                          t                          )                                                                                                                                                                                                                                  (                                                      1                            -                            β                                                    )                                                ⁢                                                                              R                            s                                                    ⁡                                                      (                            t                            )                                                                                              ⁢                                                                                                                                                                                              if                        ⁢                                                                                                  ⁢                        s                                            =                                                                        s                          n                          *                                                ⁡                                                  (                          t                          )                                                                                                                                ⁢                                                          ⁢              for              ⁢                                                          ⁢                              ∀                                  s                  ∈                                      S                    n                                                                        ,                          ∀                              n                ∈                N                                                                        [                  Equation          ⁢                                          ⁢          3                ]            
5. After t=t+1, the current step again returns to the step 1.
Inter-cell interference control means that frequency is divided to reduce interference that affects a neighboring cell, or means that the maximum available resource is reduced for a neighboring cell, for example, the available power is not used up. This does not cause a problem in solving inter-cell interference if one network provider includes several cells by installing several access points. This is because that gain occurs if a neighboring cell has better performance while using a resource of a specific cell, which is less than the maximum available resource.
However, if access points that cause interference to each other while using the same frequency band are owned by different network providers having different objects, a problem occurs in the method for controlling interference in accordance with the related art. If all the access points intend to use the maximum resource, many resources may be used but performance may be reduced due to interference.
Accordingly, although inter-cell interference control is required, it is difficult to give away resources for an access point of another network provider. In this respect, a method for improving performance on the basis of a specific contract rule, which is previously defined, while reducing damage caused by inter-cell interference, will be required.